Conventional moderate-to-high power diode-pumped lasers that use a high aspect ratio rectangular slab geometry for the active lasing medium are either end pumped, in which the pumplight traverses the slab in the same direction as the laser beam, or face pumped, in which the pumplight enters the slab through the largest face and traverses the thin dimension of the slab transverse to the beam axis. The performance of end-pumped slab lasers is limited in high power applications by the need to focus or concentrate all of the pumplight through the relatively small ends of the slab, thereby requiring high damage threshold dichroic coatings, high brightness diode arrays, and many slab segments. The design of face-pumped slab lasers for continuous lasing applications is complicated by the need to pump and cool the slab through the same large face. The aforementioned limitations of end pumping and inherent complexity of face pumping can be alleviated by transversely pumping the slab through its thin edges and cooling it through the large faces. The performance of such a simple edge pumped slab laser is limited, however, by higher absorption of the pumplight near the pumped edges of the slab and lower absorption near the center of the slab, resulting in severe gain nonuniformity. The gain nonuniformity produces highly nonuniform near-field beam profiles, high diffraction loss at beam clippers, poor far-field beam quality, gain steering of the beam, and possible optical damage due to amplification of diffraction spikes near the edge of the slab.
Some previous attempts at improving gain uniformity by reducing the doping concentration resulted in reduced pumping efficiency, as less of the pumplight was absorbed in a single pass through the slab.
Several related pump cavity designs have been proposed which provide efficient and uniform side-pumping of a laser rod or low-aspect laser slab by allowing the pumplight to traverse the laser medium in several passes, with relatively low absorption per pass. These approaches, however, are not directly applicable to high-aspect slab laser media used in moderate-to-high power applications.